Electrical tuning system



May 28,1946 v G. s. wAcl-n'lvlANV 2,400,897

ELECTRICAL TUNING SYSTEM vOriginal Filed Oct. 5. 1943 :EnEV- E fo n S40/@SW QS- waff/YMM` lBY Patented May Z8, 1946 ELECTRICAL TUNING SYSTEM George Wachtman, Harrisburg, Pa.

@riginal applicationOctober 5, 1943,` Serial No.

505,048. Divided and this application November 14, 1944, Serial No. 563,384

( Cl. Z50-40) My invention relates broadly to circuit arrangements for high frequency oscillators and more particularly to a circuit for controlling the resonant frequency of tunable circuits over a vari able frequency range with a high degree of precision,

This application is a division of my application Serial Number 505,048 for Electron tube apparatus, led October 5, 1943.

One of the objects of my invention is to provide an improved circuit arrangement for controlling the 'resonant frequency of electrically tunable circuits with a high degree of precision.

Another object of my invention is to provide a multiple dual condenser controlled variable frequency oscillator circuit including series connect ed adjustable means for compensating for the effectiveness of the respective portions of the dual condensers at any point in the frequency range of the oscillator circuit. i

Still another object of my invention is to provide a circuit arrangement for capacitively coupling ak pair of dual condensers having sections having capacities which vary simultaneously in the same direction into an oscillator circuit for the precision control of the oscillation frequency.

Other and further objects of my invention reside in the improved multiple dual condenser circuit arrangement for electrical tuning systems as set forth in the following specification and shown in the accompanying drawing in which:

Figure 1 diagrammatically shows the circuit of my invention; Fig. 2 shows a modied form of circuit arrangement embodying my invention in which greater precision may be obtained in frequency adjustment of the circuit; Fig. 3 shows the ideal characteristic curves to be obtained by the circuit of my invention; Fig. 4 illustrates the actual characteristics obtained by the circuit arrangement of my invention without the corrective features added in accordance with my invention; and Fig. 5 illustrates the characteristic curves of the circuit of my invention with the compensation system of my invention added.

Referring to the drawing in detail Figure l schematically illustrates a circuit arrangement embodying my invention by which both high and low frequency compensation is secured in the tuning system. Reference character l designates the broad tuning condenser for the circuit and reference character 2 designates the dual or split stator fine tuning condenser electrically connected with the impedance 3 as shown. The dual condenser `2 includes two sections designated at 2a and 2b which are ganged together so that their capacities vary simultaneously in the same direction. There is a single intermediate rotor and two stators associated with the intermediate rotor'and variable in positions so that the effective capacities of the two condensers thus established vary simultaneously and in the same direction. Reference characters 5 and l designate variable trimmer condensers connected in series with seotions 2a and V2b of the dual condenser 2 and connected to tap 3a on impedance 3 and to one side of the main tuning condenser I. By adjustment of condensersl 5 and 'I the control actionv of the line tuning dual condenser 2 may be adjusted. A variable condenser 8 connects between one side of main condenser I and one terminal of impedance 3 whereby the minimum or lowest tunable frequency to which the circuit will respond may be adjusted.

In the operation of the circuit as thus far described it is possible with values assigned as follows to cover frequency ranges hereinafter explained with a high degree of precision:

Variable condenser L-- 325 micro-microfarads Split stator Variable condenserZ ,.Each section 25 micromicrofarads Trimmer condenser 5 5-50 micro microfarads Trimmer condenser 1;--5-50 micro microfarads Fixed condenser 8 -'70 micro-microfarads Inductance 3 .8.5 microhenries 20 turns 1.5" in diameter x 1.375 long tapped 1/3 the distance from the grounded end By associating the elements as heretofore ex-.

plained with an oscillator system, the frequency of the circuit may be continuously varied from 5,400 kes/sec. to 9,200 kos/sec. by varying condenser I :and is also variable over a'100 kcs./sec. range by varying condenser 2 regardless of the setting of condenser I. 2a and 2b are the two sections of the dual section, ganged variable condenser 2 controlled by one dial or knob, or other control constituting a bandspread control. The range covered by the bandspread control may be varied by :adjusting trimmer condensers 5 and l. Condenser 5 controls the amount of spread at the lower frequencies while trimmer condenser 'l controls the spread at the higher frequencies. The control action exerted by both is approximately equal at mid-frequency. Condenser 3l is a dual condenser whose two sections are ganged together so that their `capacities vary simultaneously in the same direction, by means of which high and low frequency compensation is obtained. The second dual condenser or compensation control 31. is similar tothe i-lrst mentionedV dual condenser 2 in that the two sections of tne second dual condenser operates in such a way that the capacities of the two sections o1" the second vary simultaneously in the same direction much the same as the .capacities vary in the iirst, Valthough not necessarily in unison with the rst.

The capacity of condenser 8 directly affects the range covered or tuned by condenser I, more capacity increasing the range and less capacity decreasing the range,

Fig. 2 discloses a modified form of the circuit of my invention for obtaining greater precision in bandspread control. In this arrangement the parts of the circuit as described in Fig. 1 are employed with the addition of variable condensers fill and 45, interposed in series between the dual control condenser 2 and the dual control condenser 3?. The function of condensers 44 and 45 is to to adjust the amount of control condenser 31 exerts with respect to dual condenser 2. By independently adjusting condensers 44 and 45 a greater precision adjustment of the electrically Y tunable circuit is secured.

The two condenser sections 2a and 2b of the bandspread control condenser 2 always exert some control over the resonant frequency of the circuit regardless of the setting of main tuning control i. Accordingly, the ideal control characteristics as set forth in Fig. 3 for each section of the condenser 2 are never realized. Instead some resultant characteristic which is non-linear is obtained as, for example, curves A and B of Fig. 4 actually obtain for the circuit of Fig. l before the addition of dual condenser 31, curve C' being the resultant. Consequently some means of compensating for the non-linearity of curve C', Fig. 4, must be employed if accurate work is to be done with the circuit. This is accomplished by employing one or more variable condensers, or a dual section or split stator variable condenser in parallel with one or more sections of the bandspread control as shown at 31. The action of the compensating condensers is to adjust the minimum and maximum capacity of the parallel combination, thereby effectively controlling the tuning range of the bandspread control.

With the compensatingV control of Fig. 1 the ideal `resultant curve C of Fig. 3 may be ap proachecl very nearly, as shown by the curve CIV of Fig. 5. In Figs. 3, 4, and 5 the curves A, A and AIV represent the control action of the high frequency control section 2a of the bandspread control, curves B, B and B1V represent the control action of the low frequency control section 2b of the band spread control, and since the effects of the two sections 2a and 2b are additive, curves C, C and CIV represent the resultant action of curves A, B; A', B'; and AIV, BIV, respectively.

The curves of Fig, 5 illustrate the control actions and the resultant action where a split stator or dual section variable condenser 31 is employed as the compensating control for both high and low frequencies in the circuit of Fig. l.

As may readily be seen from the curves of Fig. 5, the resultant curve CIV isV identical with curve C of Fig. 3, but the separate control curves AIV and BIV only approximate curves A and B of Fig. 3, curves AIV and BIV of Fig. 5 most nearly approaching the ideal.

The uses to which the above described control circuits can be put are manifold. For example, .it can be applied to various circuits tov test lapped quartz blanks for activity and frequency to a close tolerance before they are hand-finished and put in holders. It can be used in receivers where it is desired to have a continuous bandspread of frequency; i. e., one that is constant at any setting of the main tuning control. In conjunction with a local piezo-oscillator (frequency to be determined by type of use) and a receiver, and used in a stable variable frequency generator circuit by standardizing at time of use, the circuit can be used to determine the frequency of another signal within a few cycles. This is done by heterodyning the signal emitted by the generator against the unknown signal and detecting the heterodyne beat by audible or electrical or electro-mechanical means and then reading frequency by interpolation from a known standard signal (local piezo oscillator) and the calibration on the dial of the ne tuning control. The circuit can also be used to control the frequency of the emitted radiation of a radio transmitter, allowing the frequency to be varied over a wide range, and yet, by means ci the fine tuning control and pre-standardization against a local piezo oscillator or other primary or secondary frequency standard, control the fre- Y quency within a few cycles of the desired frequency.

The applications of this invention, as can be seen from the foregoing, are almost limitless. The control circuit can be applied to any device wherein the resonant frequency is desired to be variable. It can be applied to capacity-inductance or capacity-resistance or other' impedancetuned generators or oscillators, to tuned circuits, such as radio frequency, intermediate frequency or audio frequency stages in amplifiers, receivers, filters, etc., or to other tuned circuits wherein any combination of capacity, inductance, resistance, or reactance is used.

Features of my invention shown but not claimed herein are set forth in the parent application, Serial No. 505,048, led October 5, 1943, for Electron tube apparatus, and my co-pending divisional applications Serial No. 563,383, filed November 14, 1944, for Tuning system, and Serial No. 563,385, filed November 14, 1944, for Selective tuning system.

While I have described my invention in certain of its preferred embodiments I realize that modilcations may be made and I intend no limitations upon my invention other than may be imposed by the scope of the appended claims.

What I claim as new. and desire to secure by Letters Patent of the United States is as follows:

1. An electrical tuning system comprising in combination with an impedance device, a variable tuning condenser having one side thereof connected with a point on said impedance device, a dual condenser including a central rotor and a pair of variably related capacity areas constituting a pair of condenser sections whose capacities vary simultaneously in the same direction, said rotor being electrically connected with another point of said impedance device, one of the condenser sections of said pair being disposed in series with said variable tuning condenser and theother of the condenser sections of said pair being connected effectively in parallel with the said variable tuning condenser and effectively in parallel with said impedance device, independently adjustable variable capacity means connected in series with each of the condenser sections of said dual condenser, yand means connected in shunt with each of thecondenser sections of said dual condenser for compensating for the effectiveness of the respective condenser sections at any point in the frequency range oi said tuning system.

2. An electrical tuning system comprising in combination with an impedance device, a variable tuning condenser having one side thereof connected with a point on said impedance device, a dual condenser including a central rotor and a pair of variably related capacity areas constituting a pair of condenser sections whose capacities vary simultaneously in the same direction, said rotor being electrically connected with the other end of said impedance device, one of the con ldenser sections of said pair being disposed in series with said variable tuning condenser and the other of the condenser sections of said pair being connected effectively in parallel with the said variable tuning condenser and effectively in parallel with said impedance device,` independently adjustable variable capacity means connected in series with each of the condenser sections of said dual condenser, and a second dual condenserhaving a central rotor and a pair of variably related capacity areas forming a pair of independent condenser sections, said last mentioned central rotor being electrically connected with said rst mentioned central rotor and the last mentioned independent condenser sections being electrically connected in parallel with the aforementioned condenser sections for adjustably compensating for the effectiveness of the respective condenser sections at any point in the frequency range of the tuning system.

3. An electrical tuning system comprising in combination with an impedance device, a variable tuning condenser having one side thereof con-` rotor being electrically connected with another point of said impedance device, one of the condenser sections of said pair being disposed in serieswith said variable tuning condenser and the other of the condenser sections of said pair being connected effectively in parallel with the said variable tuning condenser and effectively in parallel With said impedance device, independ ently adjustable variable capacity means connected in series With each of the condenser sections of said dual condenser, a second dual condenser having a central rotor and a pair of variably related capacity areas forming a pair of independent condenser sections, said last mentioned central rotor being electrically connected With said rst mentioned central rotor, and variable capacity means disposed in series between each of said last mentioned independent condenser sections and the aforementioned condenser sections for adjusting the amount of control said second dual condenser exerts with respect to the rst mentioned dual condenser.

GEORGE S. WACHTMAN. 

